Apparatus for forming slit in rock and concrete surface

ABSTRACT

An apparatus for forming a slit in a rock and a concrete surface has a simple construction to enable a deep slit having a predetermined width and smooth inner surface to be made efficiently and also decreases the slit making cost due to replacement of bits. This slit forming apparatus comprises a plate type bit (17) fixedly secured to the leading end of a laterally swingable plate (13), a drill bit (11) fixedly mounted on the leading end of a rod (9a and/or 9b), which is disposed along at least one side of the plate, so that it may rotate and slide, and striking means (5 and/or 12a, 12b) for striking the plate and the rod simultaneously or separately. Further, the rod has at its front end portion a stabilizer for stabilizing the direction of sliding. The plate type bit consists of a plurality of detachable bit blocks.

TECHNICAL FIELD OF THE INVENTION

This invention relates to an apparatus for making a slit shaped hole ina rock and a concrete surface, and more particularly to an apparatus forforming a slit in a rock and a concrete surface, which is provided witha swingable plate type bit having cutting edge portions mounted on theleading end thereof.

BACKGROUND ART OF THE INVENTION

In a prior art apparatus of the kind specified above for forming a slitin a rock and a concrete surface, such as the one disclosed in JapaneseLaid-Open Patent Application No. SHO 60-5996, an apparatus for making aplurality of holes uses a plurality of drills. Further, a method ofcontinuously making holes in partially overlapped relationship isdisclosed in Japanese Laid-Open Patent Application No. SHO 61-31591.

While it has been expected to develop an apparatus for forming a slitefficiently in a rock and a concrete surface, the above-mentioned priorapparatus and method have posed the following problems.

(1) A low drilling speed.

(2) A complicated construction.

(3) Because interconnected slits are formed, irregularities remain inthe inner surfaces of the slits.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedcircumstances in the prior art, and has for its object to provide anapparatus for forming a slit in a rock and a concrete surface, which hasa simple construction to enable a slit or hole having a predeterminedwidth and a smooth inner surface to be made efficiently.

Another object of the present invention is to provide an apparatus forforming a slit in a rock and a concrete surface, which has a simpleconstruction to enable a deep slit having a predetermined width and asmooth surface to be made efficiently.

A further object of the present invention is to provide an apparatus forforming a slit in a rock and a concrete surface, arranged such thatincrease in boring cost due to frequent replacement of bits can besuppressed.

To achieve the above-mentioned objects, according to a first aspect ofthe present invention there is provided an apparatus for forming a slitin a rock and a concrete surface comprising a frame supported in such amanner that it may be turned freely in the vertical direction; a slidingbase mounted on the frame in such a manner that it may be slidably movedin the longitudinal direction thereof; a striking means fixedly securedonto the sliding base and having an actuating shaft; a striking plateextending forwardly along the frame and fixedly secured to the leadingend of the shaft; two lengths of longitudinally extending rods spacedapart widthwise of the frame and in parallel with each other, each ofthe rods having one drill bit mounted on the leading end thereof; afirst support base fixedly secured to the front end portion of the frameso as to support the portions of these rods near the leading endsthereof such that they may be slidably moved forwardly in thelongitudinal direction of the frame; a second rod supporting meansfixedly mounted on the sliding base and adapted to slidably support theportions of these rods near the base or trailing ends thereof so as toallow the base ends of the two lengths of rods to contact the contactsurface of the striking plate; a plate having a plate type bit mountedon the leading end thereof, the plate being located in between the twolengths of rods such that the plate type bit is disposed somewhat behindthe drill bits when not in use and the base end of the plate is keptinto contact with the contact surface of the striking plate; and a plateswinging means for swinging the plate widthwise of the frame.

According to a second aspect of the present invention, there is providedan apparatus for forming a slit in rock or a concrete surface,characterized in that the plate type bit as set forth in the firstaspect has cutting edge portions mounted on the leading end thereof.

Further, according to a third aspect of the present invention, there isprovided an apparatus for forming a slit in a rock and a concretesurface, characterized in that the plate type bit as set forth in thefirst aspect consists of a plurality of individually detachable bitblocks.

According to a fourth aspect of the present invention, there is providedan apparatus for forming a slit in a rock and a concrete surface,characterized in that the second rod supporting means as set forth inthe first aspect comprises two sets of rotating•striking means forstriking the two lengths of rods while rotating them above theirrespective axes.

According to a fifth aspect of the present invention, there is providedan apparatus for forming a slit in a rock and a concrete surface,characterized in that the plate swinging means as set forth in the firstaspect comprises a swinging support base mounted on one side of thesliding base and adapted to support the plate so as to slidably move itby a predetermined stroke in the longitudinal direction thereof; and twosets of piston•cylinder units having piston rods capable of extensionand contraction and connected between both sides of the swinging supportbase and both sides of the sliding base so as to swing the platewidthwise of the frame about a fulcrum of swing located substantially atthe center of the swinging support base.

According to a sixth aspect of the present invention, there is providedan apparatus for forming a slit in a rock and a concrete surface,characterized in that the rear end face of the plate and the contactsurface of the striking plate which contacts the rear end face are of acircular arc shape whose center is located at the fulcrum of swing ofthe swinging support base.

Further, according to a seventh aspect of the present invention, thereis provided an apparatus for forming a slit in a rock and a concretesurface, characterized in that the plate swinging means comprises aswinging support base mounted on one side of the sliding base andadapted to support the plate so as to slidably move it by apredetermined stroke in the longitudinal direction thereof; a swing armwhose one side is fixedly secured to the swinging support base and whoseother side extends to the approximately intermediate portion of thesliding base; and one set of double-acting piston•cylinder unit mountedon the approximately intermediate part of the sliding base and connectedto the other side of the swing arm so as to swing the plate widthwise ofthe frame about the fulcrum of swing located substantially at the centerof the swinging support base.

Further, according to a ninth aspect of the present invention, there isprovided an apparatus for forming a slit in a rock and a concretesurface, characterized in that the plate swinging means as set forth inthe first aspect comprises a first holder adapted to support the plateon the front end side of the frame in such a manner that the plate maybe slidably moved in the longitudinal direction thereof; a second holderadapted to support the plate on one side of the sliding base in such amanner that the plate may be slidably moved in the longitudinaldirection thereof; a first double-acting piston•cylinder unit fixedlymounted on the frame at a position corresponding to the first holder andconnected to both sides of the first holder so as to swing the firstholder widthwise of the frame; and a second double-actingpiston•cylinder unit fixedly mounted on the sliding base and connectedto both sides of the second holder so as to swing the second holderwidthwise of the frame.

Still further, according to a tenth aspect of the present invention,there is provided an apparatus for forming a slit in a rock and aconcrete surface, characterized in that it further comprises astabilizer disposed between the drill rods mounted on the leading endsof the two lengths of longitudinally extending rods, respectively, andthe first support base as set forth in the first aspect, and adapted tosupport the two lengths of rods in such a manner that they may beslidably moved in the longitudinal direction thereof.

And, according to an eleventh aspect of the present invention, there isprovided an apparatus for forming a slit in a rock and a concretesurface, characterized in that the stabilizer as set forth in the tenthaspect is configured to pass the plate therethrough, and a piece of pinprojecting vertically upwards and downwards from the plate is engagedwith a hole formed in the central part of the stabilizer so as toconnect the plate to the stabilizer so that they may be slidably movedin synchronism with each other.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 and 2 are a schematic plan view and a schematic side elevationalview, respectively, showing a first embodiment of the present inventionin shorter length than actual;

FIGS. 3 and 4 are a schematic plan view and a schematic side elevationalview, respectively, showing a second embodiment of the present inventionin shorter length than actual;

FIGS. 5 and 6 are a schematic plan view and a schematic side elevationalview, respectively, showing a third embodiment of the present inventionin shorter length than actual;

FIG. 7 is a sectional view taken along line VII--VII in FIG. 6;

FIG. 8 is a schematic side elevational view showing operating conditionof each embodiment of the present invention;

FIGS. 9 and 10 are a schematic plan view and a schematic sideelevational view, respectively, showing a fourth embodiment of thepresent invention in shorter length than actual;

FIG. 11 is a sectional view taken along line XI--XI in FIG. 9;

FIGS. 12 and 13 are explanatory views showing conditions of two lengthsof drill rods when holes are made by drill bits according to prior artarrangement and the present invention, respectively;

FIGS. 14 and 15 are explanatory views showing the relationship betweenthe sectional area of the piston at the striking force transmittingportion and the striking energy.

FIGS. 16 and 17 are a schematic plan view and a schematic sideelevational view, respectively, showing a fifth embodiment of thepresent invention in shorter length than actual;

FIGS. 18 and 19 are a schematic plan view and a schematic sideelevational view, respectively, showing a sixth embodiment of thepresent invention in shorter length than actual;

FIGS. 20A and 20B are a front view and a plan view, respectively,showing one embodiment of a plate type bit mounted on the leading end ofa plate for use in the apparatus for forming a slit in rock or concretesurface;

FIG. 21 is a sectional view taken along line XXI--XXI in FIG. 20B; and

FIG. 22 is a plan view showing another embodiment of the plate type bitmounted on the leading end of the plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the first place, a first embodiment of the present invention will bedescribed below with reference to FIGS. 1 and 2.

In the drawings, reference numeral 1 denotes an arm; 2 a frame supportedon the leading end of the frame 1 in such a manner that it may be turnedfreely in the vertical direction; and 3 a piston•cylinder unit forturning the frame 2. Reference numeral 4 denotes a sliding base mountedslidably on the upper surface of the frame 2. This sliding base isarranged to be moved back and forth along the frame 2 by a driver meansnot shown. Reference numeral 5 indicates a striking means supportedthrough brackets 6 on the sliding base 4, and 7 an actuating shaftthereof. Reference numeral 8 indicates a striking plate mounted on theactuating shaft, which is longer widthwise and whose central part isconnected to the above-mentioned actuating shaft 7. Reference numerals9a, 9b indicate rods which are spaced apart in the transverse directionand are disposed longitudinally in parallel with each other and alsowith the frame 2. The leading ends of the rods 9a, 9b are axiallyslidably supported by a supporting base 10 fixedly mounted on the frame2. The rods 9a and 9b have drill bits 11 fixedly secured to the leadingends thereof. The bases on trailing ends of the rods 9a, 9b extendthrough rotating means 12a and 12b and are brought into contact withboth sides of the above-mentioned striking plate 8. Reference numeral 13denotes a plate which is disposed between the rods 9a and 9b. Theleading end portion of the plate 13 is supported by the above-mentionedsupporting base 10 in such a way as to slide freely widthwise andlengthwise of the frame 2. The base or trailing end of the plate 13 issupported by a swinging support base 14 in such a manner that the platemay slide a predetermined stroke in the longitudinal direction. Further,the rear end face of the plate 13 is brought into contact with the frontend face of the striking plate 8 of the striker means 5. Theabove-mentioned swinging support base 14 is supported on the slidingbase 4 in such a way as to freely swing in the horizontal direction(widthwise of the frame 2). Both sides of the swinging support base 14are connected through piston•cylinder units 15 to the sliding holder 4.The contact faces of the plate 13 and the striking plate 8 are ofcircular-arc shape whose center is located at the fulcrum of swing ofthe swinging support base 14. Fixedly secured to the front end of theplate 13 is a plate type bit 17 having built-in carbide tips 16. Theplate type bit 17 is located somewhat behind the above-mentioned drillbits 11 when not in use.

The frame 1 supporting the frame 2 is mounted on a construction vehicle18 in such a manner that it may be raised and lowered as shown in FIG.8.

The frame 2 is provided at the construction vehicle's front end with asupporting pawl 2a adapted for thrusting into a rock 19 and is fixedlysecured to the frame itself when it is pressed against the rock.

In the above-mentioned configuration, when the striking means 5 and therotating means 12a, 12b are actuated, the drill bits 9a, 9b are struckby the striking plate 8 so that they may be subjected to striking forceswhile they are being rotated by rotating means 12a, 12b. Further, theplate type bit 17 is also subjected to striking forces applied by thestriking plate 8. Furthermore, the plate type bit 17 is swunghorizontally about the fulcrum of swing O through the swinging supportbase 14 and between the drill bits 9a and 9b when the piston•cylinderunits 15 are rendered operative. Further, the above-mentioned drill bits9a, 9b and the plate type bit 17 are moved back and forth by the slidingholder 4 along the frame 2.

Rock excavating operations by using the above-mentioned apparatus willbe described below.

As shown in FIG. 8, the construction vehicle 18 is moved forward, andthe arm 1 and the frame 2 are raised or lowered so as to allow theleading ends of the drill bits 11 to thrust against the rock 19approximately at right angles thereto, and then the rotating means 12a,12b and the striking means 5 are actuated. As a result, the drill bits11 are subjected to striking forces while they are being rotated so thatthe rock 19 may be crushed or excavated. By advancing the sliding base 4simultaneously with the above operation, two horizontally spaced-apartholes are made by the two drill bits 11. When the holes are formed bythe drill bits 11 to a certain depth in the rock, the leading end of theplate type bit 17 will strike against rock 19a between theaforementioned two holes. When the plate type bit 17 strikes against therock 19a, it is swung widthwise (or horizontally) of the frame 2 and isapplied with striking forces produced by the striking plate 8, therebycrushing the rock 19a between the two holes.

As a result of the above-mentioned operations, a slit having a lengthcorresponding to the spacing between the drill bits 11 is formed in therock 19.

FIGS. 3 to 7 show second and third embodiments of the present invention.Since the component parts thereof denoted by the same reference numeralsas those used in FIGS. 1 and 2 are the same elements having the samefunctions, the description of them is omitted herein to avoidduplication of explanation.

The second and third embodiments differ from the first embodiment in theconstruction of the plate swinging means.

The second embodiment, shown in FIGS. 3 and 4, is constructed such thata swing arm 20 is fixedly secured to a swinging support base 14a, and adouble-acting piston•cylinder means 21 mounted on the sliding base 14 isconnected to the leading end of the swing arm 20. The arrangement ismade such that when the double-acting piston•cylinder unit 21 isactuated, the swinging support base 14 may be swung horizontally andwidthwise of the frame 2.

The third embodiment shown in FIGS. 5, 6 and 7 is constructed such thata plate 13, having a plate type bit 17 fixedly secured to the leadingend thereof, is supported at its front and rear portions by a firstholder 22a and a second holder 22b, respectively, as so to freely slidein the longitudinal direction of the frame 2. The front holder 22a andthe rear holder 22b are mounted through a first double-actingpiston•cylinder unit 23a and a second double-acting piston•cylinder unit23b, respectively, on the frame 2 and the sliding base 4, respectively.This allows the front and rear holders 22a and 22b to be moved by theirassociated piston•cylinder units widthwise of the frame 2. In thisembodiment, the contact faces of the plate 13 and the striking plate 8aare kept in parallel with the direction of movement of the plate 13.

Next, the fourth embodiment of the present invention will be describedwith reference to FIGS. 9 to 11.

In this fourth embodiment too, the component parts thereof indicated bythe same reference numerals and characters as those used in the first,second and third embodiments are the same elements having the samefunctions. Therefore the description of them is omitted herein to avoidduplication of explanation.

In this fourth embodiment, rods 9a and 9b, which have drill bits 11,mounted on the leading ends thereof, are disposed on both sides of theplate 13 and have their base or trailing ends thereof connected to theirrespective rotating•striking means 12a, 12b, respectively. The rear endface of the plate 13, having a plate-type pit 17 at the leading endthereof, is brought into contact with the leading end face of a strikingplate 8 of a striking means 5, as in the above-mentioned embodiments.Thus, the drill bits 11 and the plate type bit 17, may be struckindependently. As a result, excellent transmission of striking forces tothe drill bits 11 can be achieved so that the boring operation can bemade smoothly. With regard to the plate type bit 17, the striking plate8 can be made smaller in size and lighter in weight so that the size ofthe striking force transmitting member can be made smaller.

Further, in this fourth embodiment, a stabilizer 24 is mounted on thedrill bits 9a, 9b, in front of a support base 10, which supports theleading end portions of the plate 13 and the rods 9a, 9b, respectively.The stabilizer is placed between the support base 10 and the plate typebit 17, in order to keep the distance between the rods 9a and 9bconstant.

As shown in FIG. 11, the stabilizer 24 slides on the rods 9a and 9b andhas the following operational relationship with the plate 13. Hereupon,the stabilizer 24 has a hollow portion 24a which is formed in theintermediate portion thereof and through which the plate 13 can freelyslide in the direction of swing thereof. Further, since a pin 25projecting vertically up and down from the plate 13 engages with theedges of the minor axis of an elliptical hole 24b formed through thestabilizer 24. When the plate 13 is moved in the longitudinal directionthereof, the stabilizer 24 slides along the rods 9a, 9b, with the plate13.

In a slit forming operation, as the slit becomes deeper, the drill rods9a, 9b are thrust further from the support base 10, and as a result, theleading end side portions of the drill rods 9a, 9b become unstable. Thuswhen the drill bits 11 are subjected to unequal loads, due to formationof cracks in the rock 19 and uneven quality thereof, the spacing L'between the leading ends of the drill rods 9a and 9b may become widerthan the normal spacing L, as shown in FIG. 12. This renders itimpossible to keep the normal spacing L. In such a case, the spacingbetween the two holes made by the drill bits 11 becomes wider than theexcavation width of the hole made by the plate type bit 17 thus leavingportions 19b, 19b which are not. This creates discontinuity between theleft and right holes and the central hole which may render it impossibleto make an intended hole.

Thereupon, in the fourth embodiment, as the slit being formed becomesdeeper and the sliding base is moved forward so that the drill rods 9a,9b and the plate 13 are thrust away from the support base 10, thestabilizer 24 is also moved away at the same time. As a result, as shownin FIG. 13, the drill bits 9a and 9b are always supported by thestabilizer 24 at the same positions from the drill bits 11. Therefore,even when the depth of the hole becomes deeper, the spacing between thedrill bits 11 can always be maintained at the normal value L regardlessof excavating conditions.

Further, it is desirable to make the sectional area of the strikingplate 8 equal to that of the piston for the striking means 5. It isdifficult, however, achieve this in practice.

We have made experimental studies and the results are summarized asfollows.

It was found out that if the ratio of sectional area between thestriking plate 8 and the piston of the striking means is in the range of0.5 to 2.0, then about 90% or more of the kinetic energy, or thestriking energy, produced by the piston in the striking means 5 can betransmitted to the striking plate 8. FIGS. 14 and 15 show theabove-mentioned experimental result wherein A₁ denotes the area of thepiston, A₂ the area of the striking energy transmitting member, E₁ thekinetic energy developed by the piston, and E₂ the kinetic energy of thestriking energy transmitting member. With a higher energy transmissionratio (E₂ /E), more of the striking energy is transmitted.

FIGS. 16 and 17 show the fifth embodiment which is a modification of thefourth embodiment.

Reference numerals 26 indicate a plurality of holes made previously inrows at regular intervals in a rock by means of a boring device notshown. These drawings show an apparatus for use in forming a slitbetween the adjoining holes. In this slit forming apparatus, theprovision of drill bits is not necessary and desired slits can be formedonly by the plate type bit alone. Further, it is possible to forminterconnected slits.

FIGS. 18 and 19 show a further modification of the above-mentionedfourth embodiment.

This modified embodiment comprises a striking means 5 for drilling theportion of a rock between previously made holes and a rotating•strikingmeans 12a for use with a piece of drill rod 9a.

An interconnected slit forming operation using this modified embodimentis made as follows.

A preliminary hole 27, which serves as the starting point, is made bymeans of a boring device, not shown, and then a second hole 28 is madeby the drill rod 9a at a position spaced from the hole 27 by a distancewhich is nearly equal to the transverse width of the plate type bit 17.Thereafter, the rock or concrete surface between the holes 27 and 28 iscrushed by the plate type bit 17 to form a slit. In case interconnectedslits are formed, it is only necessary to repeat the above-mentionedoperation.

FIGS. 20A, 20B and 20C show another embodiment of the plate type bit 17.

As shown in FIG. 20B, the plate 13 has a right hand tongue 13a, acentral tongue 13b and a left hand tongue 13c formed at the leading endportion in juxtaposition.

The plate type bit 17 is comprised of three pieces of bit blocks, i.e. aright hand bit block 17a, a central bit block 17b, and a left hand bitblock 17c. These bit blocks 17a, 17b and 17c have mounting holes 31a,31b and 31c formed in the rear portions thereof, respectively. Byfitting the tongues of the plate 13 into their respective mounting holesand connecting them by means of pins 32, each of the bit blocks can bedetachably mounted on the leading end of the plate 13.

Further, the bit blocks 17a, 17b and 17c are formed at their respectiveleading edges with cutting edge portions 30a, 30b and 30c, respectively,each having a plurality of carbide tips.

Thus, the use of the plate type bit 17 comprised of a plurality of bitblocks results in a considerable reduction in maintenance cost due toreplacement of parts.

In case, for example, the cutting edge portion 30a of the right hand bit17a is partially broken off, it is only necessary to replace the righthand bit block 17a while leaving the central and left hand bit blocks17b and 17c as they are. Since the size of the right hand bit block 17ais about one third of that of the whole plate type bit 17, itsmanufacturing cost is low as compared with the cost of an integratedtype bit, which is not split into several parts.

FIG. 22 shows a modification of the above-mentioned split-typeplate-shaped bit 17. Hereupon, the plate-type bit 17 in this modifiedembodiment comprises two-split bit blocks, i.e. a bit block 13a and abit block 13b. Since this embodiment is identical in terms of otherarrangements to that shown in FIGS. 20A, 20B and 21, detaileddescription thereof is omitted herein.

Further, the number of divisions of the bit block is not limited to twoand three as in the case of the above-mentioned embodiments and can beset properly so as to meet the requirements, such as the size of theplate type bit, etc.

Further, the cost for replacement of parts can be reduced by using aplurality of bit blocks and also mounting in built-in fashion aplurality of split edge portions (not shown) on the leading end of eachof the bit blocks by the bit block group.

The foregoing description is merely illustrative of preferredembodiments of the present invention, and the scope of the presentinvention is not to be limited thereto. Many other changes andmodifications of the present invention will readily occur to thoseskilled in the art without departing from the scope of the presentinvention described in the appended claims.

What is claimed is:
 1. An apparatus for forming a slit in a rock and a concrete surface comprising: a frame supported in such a manner that it may be turned freely in the vertical direction; a sliding base mounted on the frame in such a manner that it may be slidably moved in the longitudinal direction thereof; a striker means fixedly secured onto the sliding base and having an actuating shaft; a striker plate extending forwardly along said frame and fixedly secured to the leading end of the shaft; two lengths of longitudinally extending rods spaced apart widthwise of said frame and in parallel with each other, each of the rods having one drill bit mounted on the leading end thereof; a first support base fixedly secured to the front end portion of said frame so as to support the portions of these rods near the leading ends thereof such that they may be slidably moved forwardly in the longitudinal direction of said frame; a second rod supporting means fixedly mounted on said sliding base and adapted to slidably support the portions of these rods near the base or trailing ends thereof so as to keep the base ends of said two lengths of rods in contact with the contact surface of said striker plate; a plate having a plate type bit mounted on the leading end thereof, said plate being located in between said two lengths of rods such that the plate type bit is disposed somewhat behind said drill bits when not in use and the base end of the plate is kept into contact with the contact surface of said striker plate; and a plate swinging means for swinging the plate widthwise of said frame.
 2. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 1, characterized in that said plate type bit has cutting edge portions mounted on the leading end thereof.
 3. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 2, characterized in that said plate type bit consists of a plurality of individually detachable bit blocks.
 4. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 1, characterized in that said second rod supporting means comprises two sets of rotating•striking means for striking said two lengths of rods while rotating them about their respective axes.
 5. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 1, characterized in that said plate swinging means comprises a swinging support base mounted on one side of said sliding base and adapted to support said plate so as to slidably move it by a predetermined stroke in the longitudinal direction thereof; and two sets of piston•cylinder units having piston rods capable of extension and contraction and connected between both sides of said swinging support base and both sides of said sliding base so as to swing said plate widthwise of said frame about a fulcrum of swing located substantially at the center of the swinging support base.
 6. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 5, characterized in that the rear end face of said plate and the contact surface of said striking plate which contacts the rear end face are of a circular arc shape whose center is located at the fulcrum of swing of said swinging support base.
 7. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 1, characterized in that said plate swinging means comprises a swinging support base mounted on one side of said sliding base and adapted to support said plate so as to slidably move it by a predetermined stroke in the longitudinal direction thereof; a swing arm whose one side is fixedly secured to the swinging support base and whose other side extends to the approximately intermediate portion of said sliding base; and one set of double-acting piston•cylinder units mounted on the approximately intermediate part of said sliding base and connected to the other side of said swing arm so as to swing said plate widthwise of said frame about the fulcrum of swing located substantially at the center of said swinging support base.
 8. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 7, characterized in that the rear end face of said plate and the contact surface of said striking plate which contacts the rear end face are of a circular arc shape whose center is located at the fulcrum of swing of said swinging support base.
 9. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 1, characterized in that said plate swinging means comprises a first holder adapted to support said plate on the front end side of said frame in such a manner that the plate may be slidably moved in the longitudinal direction thereof; a second holder adapted to support said plate on one side of said sliding base in such a manner that the plate may be slidably moved in the longitudinal direction thereof; a first double-acting piston•cylinder unit fixedly mounted on said frame at a position corresponding to said first holder and connected to both sides of the first holder so as to swing the first holder widthwise of said frame; and a second double-acting piston•cylinder unit fixedly mounted on said sliding base at a position corresponding to said second holder and connected to both sides of the second holder so as to swing the second holder widthwise of said frame.
 10. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 1, characterized in that that it further comprises a stabilizer disposed between the drill bits mounted on the leading ends of said two lengths of longitudinally extending rods, respectively, and said first supporting base, and adapted to support said two lengths of rods in such a manner that they may be slidably moved in the longitudinal direction thereof.
 11. An apparatus for forming a slit in a rock and a concrete surface as claimed in claim 10, characterized in that said stabilizer is configured to pass said plate therethrough, and a piece of pin projecting vertically upwards and downwards from the plate is engaged with a hole formed in the central part of the stabilizer so as to connect said plate to said stabilizer so that they may be slidably moved in synchronism with each other. 